The present invention relates to drills suitable for deep hole drilling and having helical or straight flutes formed in the shank for discharging chips therethrough.
Generally, drills are formed with helical flutes in the shank for discharging chips. The chips are curled while moving through the flutes and are discharged in the form of conical helical chips. Such discharged chips revolve with the rotation of the drill, wind around neighboring portions of the drilling apparatus and therefore cause trouble when the apparatus is operated automatically continuously in the absence of the operator. Attempts are also made to cause drills to produce chips in the form of small fragments instead of forming continuous chips. Further to discharge chips smoothly, conventional drills are formed with enlarged flutes for curled chips to pass therethrough easily.
In the case where chips are thus discharged as curled, there arises the problem that the chips are cumbersome to remove. Especially, deep hole drilling encounters the problem that chips clog up the flute without being discharged smoothly to make it impossible to conduct the drilling operation.
Further when large flutes are formed to discharge chips smoothly, there arises the problem that the shank has reduced torsional rigidity, failing to drill holes efficiently.
Deep hole drilling, which involves the necessity of supplying oil to the cutting portion, encounters another problem. When the oil is supplied through the flute from outside, the chip moves up while curling to the shape of a funnel to scoop up the oil supplied to the flute, with the result that the oil fails to reach the cutting portion. To overcome this problem, conventional twist drills are produced by a complex method, i.e., by forming an axial bore in a shank, then twisting the shank and forming oil supply ports.
The main object of the present invention, which has been accomplished to eliminate these drawbacks of the prior art, is to provide a drill having shallow chip discharge flutes generally L-shaped in cross section, given improved rigidity and permitting chips to be discharged smoothly while being prevented from continuously curling without the necessity of forming the flutes to a greater depth even for use in deep hole drilling, the drill further being so adapted that the chips produced spontaneously breaks when egressing from the hole formed by the drill or when leaving the drill.